Tooth pulp pain is considered a good model for human pain studies because it resembles clinical pain. Ozick's technique of delivering electrical stimulation to the dental pulp has been modified to be similar to the laboratory pain-induction methods along other sensory modalities used routinely by the NYU Pain Research Group. These psychophysical methods measure pain threshold, drug request point, pain tolerance and pain sensitivity range. In addition, we are testing if a non-painful sensation can also be measured by tooth pulp stimulation. The modified Ozick technique will be evaluated for its reliability and validity and for its sensitivity to analgesic drugs. Aspirin, codeine and placebo will be used in cross-over studies. Pain response parameters obtained with the tooth pulp stimulation technique will be correlated with those obtained from other standardized pain-induction methods utilizing chemical, electrical, mechanical and thermal noxious stimuli. These correlations, together with those obtained from two personality questionnaires, will be factor analyzed in order to isolate a specific pain factor, termed pain endurance by Wolff. Finally, classical psychophysical methodology will be compared with and contrasted to signal detection techniques in the pain area, using tooth pulp stimulation. Paid, healthy, adult volunteers will be used for all studies.